/street-design

name: street-design
description: >-
  Design complete streets with proper cross-sections, lane allocation,
  pedestrian and cycling infrastructure, intersection design, and streetscape
  elements using NACTO and global standards. Use when the user asks to design a
  street, create a cross-section, determine road width, design an intersection,
  plan a bike lane, design a sidewalk, create a boulevard, design a shared
  street, plan traffic calming, or specify streetscape elements. Also use for
  street hierarchy classification, right-of-way allocation, or any question
  about street dimensions and standards.

Street Design Skill

This skill provides comprehensive street design guidance based on NACTO Urban Street Design Guide, Global Designing Cities Initiative (GDCI), AASHTO Green Book, and international best practices. It covers the full workflow from street hierarchy classification through cross-section dimensioning, intersection design, streetscape specification, and traffic calming.

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1. Street Hierarchy Classification

Use the following decision tree to classify any street. Start with the Average Daily Traffic (ADT) count, then apply contextual modifiers.

Primary Classification by ADT and Function

**Arterial (>15,000 ADT)**

• Right-of-Way (ROW): 30-40m
• Lanes: 2-3 per direction (3.0-3.3m each)
• Design speed: 40-50 km/h (urban), 50-60 km/h (suburban)
• Transit: dedicated bus/BRT lanes strongly recommended
• Cycling: protected bike lanes required (physically separated)
• Pedestrian: wide sidewalks 3.6-6.0m, pedestrian refuge islands at crossings
• Median: 3.0-6.0m landscaped or transit median
• Signal spacing: 200-400m typical
• Role: city-wide movement, connects districts, carries transit trunk routes

**Collector (3,000-15,000 ADT)**

• ROW: 22-30m
• Lanes: 1-2 per direction (3.0-3.3m each)
• Design speed: 30-40 km/h
• Transit: on-street bus stops with boarding islands
• Cycling: protected bike lanes or buffered bike lanes
• Pedestrian: generous sidewalks 2.4-3.6m
• Median: optional, 1.8-3.0m where present
• Role: connects neighborhoods to arterials, local commercial corridors

**Local Street (<3,000 ADT)**

• ROW: 15-22m
• Lanes: 1 per direction (2.7-3.0m each)
• Design speed: 30 km/h
• Transit: typically no fixed-route transit
• Cycling: shared lane markings (sharrows) or separated bike lanes depending on context
• Pedestrian: standard sidewalks 1.8-2.4m
• Parking: parallel one or both sides
• Role: neighborhood access, residential frontage, low-speed environment

**Shared Street / Woonerf (<1,000 ADT)**

• ROW: 8-15m
• Lanes: single surface, no lane markings
• Design speed: 10-20 km/h
• Cycling: shared surface, cyclists and pedestrians together
• Pedestrian: priority over vehicles, no curb separation
• Surface: textured paving, bollards, planters as speed controls
• Role: residential living streets, market streets, festival routes

**Pedestrian Priority Street (variable ADT, typically <500)**

• ROW: variable (4-20m)
• Vehicles: no through-traffic, emergency and service access only
• Design speed: 5-10 km/h (service vehicles only)
• Surface: high-quality paving, level, no curbs
• Role: retail promenades, civic spaces, historic cores

Contextual Modifiers

Apply these modifiers after primary classification to adjust cross-section priorities:

| Context | Modifier | |---------|----------| | **Commercial / Retail** | +1.2-2.4m sidewalk width, continuous retail frontage, on-street parking or loading zones, wider furnishing zone for outdoor dining | | **Residential** | Prioritize tree canopy coverage (>40%), reduce travel lane widths to minimum, add traffic calming, reduce noise through surface treatment | | **Mixed-Use** | Adaptive curbside management (flex zones for parking/loading/transit by time of day), wider pedestrian zones at ground-floor retail | | **Industrial / Logistics** | Wider travel lanes (3.3-3.6m) for trucks, larger corner radii, reinforced pavement, limit pedestrian/cyclist exposure to truck movements | | **School Zone** | 20-30 km/h speed limit, raised crossings at every intersection, flashing beacons, wide clear sidewalks, no on-street parking within 30m of entrance | | **Hospital / Institutional** | Accessible design priority, generous drop-off zones, clear wayfinding, audible pedestrian signals, level surfaces throughout | | **Historic District** | Narrower ROW acceptable, special materials and furnishings, heritage lighting, preservation of existing tree canopy and setbacks | | **Waterfront / Park Edge** | Wider promenade (4.5-6.0m+), separated multi-use path, enhanced landscape buffer, view corridor preservation |

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2. Cross-Section Design Methodology

Design cross-sections layer by layer, working from the building face toward the street centerline. Each layer has a defined function and dimensional range.

Layer Sequence (Building Face to Centerline)

BUILDING FACE
  |
  |--> [A] Building Setback (context-dependent)
  |--> [B] Frontage Zone (0.3 - 0.9m)
  |--> [C] Pedestrian Clear Zone (1.8 - 3.6m)
  |--> [D] Furnishing / Planting Zone (0.6 - 1.8m)
  |--> [E] Cycle Track + Buffer (optional: 1.5-2.5m track + 0.3-0.6m buffer)
  |--> [F] Parking Lane (optional: 2.1 - 2.4m parallel, 4.5-5.5m angled)
  |--> [G] Travel Lane(s) (3.0 - 3.3m each)
  |--> [H] Median (optional: 1.2 - 6.0m)
  |
  CENTERLINE (mirror layers G through A for opposite side)

Layer Definitions

**[A] Building Setback** Not part of the public ROW but affects street enclosure. Zero setback for urban retail frontage, 1.5-3.0m for residential, 3.0-6.0m+ for suburban or institutional.

**[B] Frontage Zone (0.3 - 0.9m)** The strip immediately adjacent to the building face. Accommodates door swings, window displays, awning drip lines, basement vault covers. In commercial areas, may include outdoor dining or merchandise display (with permit, requiring wider dimension of 1.2-2.4m).

**[C] Pedestrian Clear Zone (1.8 - 3.6m)** The unobstructed walking path.